1. Field of the Invention
This invention relates to a sheet workpiece manipulating device for a bending press.
2. Description of the Prior Art
Conventional sheet workpiece manipulating device for a bending press is provided with a device for gripping a sheet workpiece in front of the bending machine, and a supporting member mounted on a front frame of the bending press, for supporting the gripping device in a manner such that the sheet workpiece gripped by the gripping device is moved along three cartesian axes, and rotated about two perpendicular axes (see, for example, U.S. Pat. No. 4,829,757).
With this conventional sheet workpiece manipulating device, a sheet workpiece can be positioned at a desired position with respect to a bending tool of the bending press, and can be turned over so as to be subjected to a reverse bending operation.
In addition, with the help of an auxially manipulator, which is mounted on a side section of the bending machine, the above manipulator can provide, for example, all of the four edges of a rectangular sheet workpiece to the bending machine, whereby a box-like product is produced.
However, such conventional sheet workpiece manipulating device is not suitable for handling a large workpiece.
Conventional gripping devices, which is provided, for example, on a sheet workpiece manipulating device such as the above, includes motor-driven arms carrying gripping structures that may be provided with a plurality of suction cups connected to a vacuum source. In order to grip a sheet, the structure is placed on the surface of the sheet to be lifted and the suction cups are then connected to the vacuum source. Devices of this type do not lend themselves to gripping metal sheets in which holes have already been made, since the suction cups obviously lose their effectiveness if they are situated in correspondence with a hole. Moreover, a metal sheet gripped by means of suction cups is quite unstable due to the resilience of the suction cups.
For a gripping device mounted on the manipulating device, mechanical gripping devices are also known and include one or more motor-driven manipulating grips for gripping a sheet at one of its edges. In this case, the support arms of the manipulating grips must be sized to withstand the gripping force of the grips, as well as to bear the weight of the metal sheet and the dynamic stresses resulting from its movement.